中国沿海洛氏角毛藻复合群的多样性组成及地理分布

Species diversity and geographical distribution of the Chaetoceros lorenzianus complex along the coast of China

洛氏角毛藻复合群(Chaetoceros lorenzianus complex)指具有与洛氏角毛藻相似形态学特征的物种集合,它们广泛分布于全球近岸水域。近年国际上关于该复合群的分类学研究取得新进展,而我国相关研究仍较为滞后。为了弄清我国沿海洛氏角毛藻复合群的物种多样性,明确物种信息,厘清种间界限,为相关研究提供准确的物种鉴定依据,本研究陆续在中国沿海建立了该复合群的332个单克隆培养株系,利用光学显微镜、扫描电镜和透射电镜进行了较为详尽的形态学研究,基于核糖体大亚基编码基因D1–D3区序列,构建了分子系统学关系。结果表明其形态聚类与分子系统学结论相一致,显示我国洛氏角毛藻复合群具有较高的物种多样性,共鉴定到5个物种,分别是并基角毛藻(C.decipiens)、优美角毛藻(C.elegans)、平孢角毛藻(C.laevisporus)、曼纳角毛藻(C.mannaii)和稀树角毛藻(C.pauciramosus)。研究表明传统认知的光镜下特征,如群体特征、角毛走势等易变化,其分类学价值需谨慎应用。角毛的超微结构,如角毛孔纹的形状、大小、密度等是有效的种间区别特征,休眠孢子亦是重要的物种识别依据。并基角毛藻和平孢角毛藻在我国沿岸的分布范围最为广泛,而稀树角毛藻的分布较为有限。

The Chaetoceros lorenzianus complex is composed of several planktonic diatom species that share a similar morphology with C.lorenzianus Grunow.The complex has been recorded frequently in coastal waters across the world.Recently,new taxonomic information has enriched the known species diversity of the complex from 3 to 7 taxa.However,the identities of many species comprising the complex in China is still unclear.To clarify the species diversity and provide solid identification criteria for further studies,332 monoclonal strains belonging to the C.lorenzianus complex were collected from the coast of China.With light microscopy and scanning and transmission electron microscopy,the morphologies of vegetative cells and resting spores were observed.Hypervariable D1–D3 regions of nuclear large subunit ribosomal encoded genes were amplified to construct the phylogenetic relationship.Morphological clustering was consistent with molecular systematics,which indicated that a total of 5 species are present within the C.lorenzianus complex along the coast of China;C.decipiens,C.elegans,C.laevisporus,C.mannaii and C.pauciramosus.The ultrastructure on setae,such as the shape,size and density of the setae pores,can be used as distinguishing features among allied taxa.The morphology of the resting spores also aid in accurate identification.The previous reports identifying the taxa within the C.lorenzianus complex in China need to be reexamined.Chaetoceros decipiens and C.laevisporus are the most widespread taxa along the coast of China,whereas C.pauciramosus has the narrowest distribution,having only been recorded in Taishan and Zhuhai of the Guangdong Province.